Structural and electrical properties of laser-crystallized nanocrystalline Ge films and nanocrystalline Ge/SiN_x multilayers

Nanocrystalline Ge (nc-Ge) single layers and nc-Ge/SiN_x multilayers are prepared by laser annealing amorphous Ge (a-Ge) films and a-Ge/SiN_x multilayers. The microstructures as well as the electrical properties of laser-crystallized samples are systematically studied by using various techniques. It is found that the optical band gap of nc-Ge film is reduced compared with its amorphous counterpart. The formed nc-Ge film is of p-type, and the dark conductivity is enhanced by 6 orders for an nc-Ge single layer and 4 orders for a multilayer. It is suggested that the carrier transport mechanism is dominant by the thermally activation process via the nanocrystal, which is different from the thermally annealed nc-Ge sample at an intermediate temperature. The carrier mobility of nc-Ge film can reach as high as about 39.4 cm²·V^-1·s^-1, which indicates their potential applications in future nano-devices.